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llvm-project/llvm/test/CodeGen/X86/switch-order-weight.ll

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SelectionDAGBuilder: When emitting small compare chains for switches order them by using edge weights. SimplifyCFG tends to form a lot of 2-3 case switches when merging branches. Move the most likely condition to the front so it is checked first and the others can be skipped. This is currently not as effective as it could be because SimplifyCFG destroys profiling metadata when merging branches and switches. Merging branch weight metadata is tricky though. This code touches at most 3 cases so I didn't use a proper sorting algorithm. llvm-svn: 157521
2012-05-27 04:01:32 +08:00
; RUN: llc -mtriple=x86_64-apple-darwin11 < %s | FileCheck %s
; Check that the cases which lead to unreachable are checked after "10"
define void @test1(i32 %x) nounwind uwtable ssp {
entry:
switch i32 %x, label %if.end7 [
i32 0, label %if.then
i32 10, label %if.then2
i32 20, label %if.then5
]
Convert CodeGen/*/*.ll tests to use the new CHECK-LABEL for easier debugging. No functionality change and all tests pass after conversion. This was done with the following sed invocation to catch label lines demarking function boundaries: sed -i '' "s/^;\( *\)\([A-Z0-9_]*\):\( *\)test\([A-Za-z0-9_-]*\):\( *\)$/;\1\2-LABEL:\3test\4:\5/g" test/CodeGen/*/*.ll which was written conservatively to avoid false positives rather than false negatives. I scanned through all the changes and everything looks correct. llvm-svn: 186258
2013-07-14 04:38:47 +08:00
; CHECK-LABEL: test1:
SelectionDAGBuilder: When emitting small compare chains for switches order them by using edge weights. SimplifyCFG tends to form a lot of 2-3 case switches when merging branches. Move the most likely condition to the front so it is checked first and the others can be skipped. This is currently not as effective as it could be because SimplifyCFG destroys profiling metadata when merging branches and switches. Merging branch weight metadata is tricky though. This code touches at most 3 cases so I didn't use a proper sorting algorithm. llvm-svn: 157521
2012-05-27 04:01:32 +08:00
; CHECK-NOT: unr
; CHECK: cmpl $10
; CHECK: cmpl $20
Distribute the weight on the edge from switch to default statement to edges generated in lowering switch. Currently, when edge weights are assigned to edges that are created when lowering switch statement, the weight on the edge to default statement (let's call it "default weight" here) is not considered. We need to distribute this weight properly. However, without value profiling, we have no idea how to distribute it. In this patch, I applied the heuristic that this weight is evenly distributed to successors. For example, given a switch statement with cases 1,2,3,5,10,11,20, and every edge from switch to each successor has weight 10. If there is a binary search tree built to test if n < 10, then its two out-edges will have weight 4x10+10/2 = 45 and 3x10 + 10/2 = 35 respectively (currently they are 40 and 30 without considering the default weight). Each distribution (which is 5 here) will be stored in each SwitchWorkListItem for further distribution. There are some exceptions: For a jump table header which doesn't have any edge to default statement, we don't distribute the default weight to it. For a bit test header which covers a contiguous range and hence has no edges to default statement, we don't distribute the default weight to it. When the branch checks a single value or a contiguous range with no edge to default statement, we don't distribute the default weight to it. In other cases, the default weight is evenly distributed to successors. Differential Revision: http://reviews.llvm.org/D12418 llvm-svn: 246522
2015-09-01 09:42:16 +08:00
; CHECK: bar
SelectionDAGBuilder: When emitting small compare chains for switches order them by using edge weights. SimplifyCFG tends to form a lot of 2-3 case switches when merging branches. Move the most likely condition to the front so it is checked first and the others can be skipped. This is currently not as effective as it could be because SimplifyCFG destroys profiling metadata when merging branches and switches. Merging branch weight metadata is tricky though. This code touches at most 3 cases so I didn't use a proper sorting algorithm. llvm-svn: 157521
2012-05-27 04:01:32 +08:00
if.then:
tail call void @unr(i32 23) noreturn nounwind
unreachable
if.then2:
tail call void @bar(i32 42) nounwind
br label %if.end7
if.then5:
tail call void @unr(i32 5) noreturn nounwind
unreachable
if.end7:
ret void
}
declare void @unr(i32) noreturn
declare void @bar(i32)